In a mobile communication system, while a system band is further broadened with a rapid increase of traffic, there are issues one of which is to increase spectrum efficiency, i.e., efficiency in use of frequency spectra that are limited resources. In communication systems, such as LTE (Long Term Evolution) and LTE-A (LTE-Advanced), in accordance with 3GPP (Third Generation Partnership Project), standardization has recently been progressed on the premise of FDMA (Frequency Division Multiple Access), which is one of access techniques to avoid interference among terminal devices (also called intra-user interference) in communications between a base station device (such as a base station, a transmitting station, a transmitting point, a downlink transmitting device, an uplink receiving device, a transmit antenna group, a transmit antenna port group, or eNodeB) and a plurality of terminal devices by usually keeping orthogonality among the terminal devices.
In 3GPP LTE Rel. 8, for example, OFDM (Orthogonal Frequency Division Multiplexing) is used in a down line (communication from a base station device to a terminal device), and DFT-S-OFDM (Discrete Fourier Transform Spread OFDM) is specified for an up line (communication from the terminal device to the base station device).
Recently, NOMA (Non-Orthogonal Multiple Access) techniques of allocating the same time, frequency and spatial resources (precoding in the same space) to a plurality of terminal devices and transmitting signals in a non-orthogonally multiplexed state have been studied with intent to increase a system capacity and to improve communication opportunities (see Non Patent Literature (NPL) 1). In NOMA, inter-user interference generates because the signals to be sent from the base station device to the plurality of terminal devices are transmitted in the non-orthogonally multiplexed state by Superposition Coding (SC, also called SCM: Superposition Coded Modulation), for example. Accordingly, the terminal device is needed to cancel or suppress the inter-user interference. As techniques for cancelling the inter-user interference, there are, for example, CWIC (Codeword Level Interference Cancellation) that removes the interference by employing a decoding result of an interference signal, and SLIC (Symbol Level Interference Cancellation) that removes the interference by employing an interference signal before decoding. MLD (Maximum Likelihood Detection) can also be applied as a signal detection method in NOMA.